This invention relates to a windmill of the vertical shaft type, which uses a self-adjusting sail or sails to catch the wind on one side of the mill and the same self adjusting design of the sail or sails to reduce the profile of the sail or sails and thus the resistance on the opposite side of the mill to near zero. The mill is designed to catch low velocity wind efficiently, turn at relatively low speed, and produce high torque, as well as be able to relieve itself from winds that are too severe. The only other windmills of similar design that I am aware of are wind speed indicators and wind turbines designed as vents. These are vertical shaft windmills of a fixed design. These former designs have too much reverse resistance, require too much material for construction, and are unable to relieve themselves from winds that are too severe.